The present invention relates generally to a computer system in which the central processing unit (CPU) may be upgraded. More specifically, the computer system of the present invention is designed for compatibility between 32-bit and 64-bit processors as well as between single and multi-processor systems.
With the rapid pace of development in CPU technology, obsolescence is a problem to both the manufacturers and the users of personal computers. A product which employs state of the art technology at the time of its initial marketing may become obsolete within a year or less. Personal computers employing 80286 CPUs are current examples. These obsolete computer systems remain operable, but often lack the capability of running software designed for use with systems having more advanced CPUs. In order to run such software on their existing hardware, users are forced to upgrade their systems, and in the process are faced with the following questions: Given a particular system's application, what level of upgrade is required to keep abreast of the current developments in processor and software technology (e.g., would an 80386 provide sufficient computing power, or is an upgrade to a more powerful processor, an 80486 for example, necessary)? What is the most economical way to expand a computer system from a single processor system to a multi-processor computer system in the event that the computing power of a single processor system is insufficient?
There are existing alternatives to the impractical solution of buying a new computer each time a new CPU is developed. One solution involves providing a specially designed CPU circuit board in the original system on which a prepared location (e.g., an IC socket) is provided for inserting a second CPU when the original CPU on the board requires an upgrade. Upon insertion of the new CPU into the prepared location, the original CPU is disabled. Such a specially designed circuit board is described in copending U.S. patent application Ser. No. 07/872,611 for Upgradeable/Downgradeable Central Processing Unit Chip Computer System, filed on Apr. 22, 1992, and copending U.S. patent application Ser. No. 07/998,879 for Single Chip Replacement Upgradeable/Downgradeable Data Processing System, filed on Dec. 28, 1992, both of which are herein incorporated by reference in their entirety. Commonly assigned U.S. patent application Ser. No. 07/689,317 filed on Apr. 22, 1991 and U.S. patent application Ser. No. 07/748,780 filed on Aug. 22, 1991, both also describe approaches for upgrading a computer system's CPU.
However, while various design options for upgrading CPUs are available, computer systems which can easily switch from a 32-bit CPU (e.g., 80386, 80486) to a 64-bit CPU (e.g., Intel's Pentium (p5)) are lacking. This is largely due to the incompatibility of a 32-bit wide data path and a 64-bit processor. Furthermore, no computer systems are presently available which may be upgraded from a lower generation single-processor to a higher generation multi-processor simply by swapping a CPU module and/or inserting an extra CPU.
In view of the foregoing, there is a need for a computer system in which the user may easily upgrade the system's CPU from a 32-bit processor to a 64-bit processor merely by changing CPU modules in a module interface slot built into the main circuit board. It is further desirable that such a system facilitates not only upgrades from 32-bit processing to 64-bit processing, but also from a single-processor system to a multi-processor system.